Corneal anatomy

New approaches to difficult corneal pathologies follow anatomic discoveries

TBC Soosan Jacob

Posted: Thursday, March 1, 2018

Harminder Dua MD, PhD

New understanding of the anatomy of the cornea has led to the development of new interventional strategies to challenging corneal pathologies, Harminder Dua MD, PhD, told the World Congress of Paediatric Ophthalmology and Strabismus in Hyderabad, India.

Prof Dua, Chair and Professor of Ophthalmology, University of Nottingham, Queen’s Medical Centre, Nottingham, UK, discussed this topic during his keynote speech after receiving the Kanski Medal.

Prof Dua reviewed the research leading to the discovery of the pre-Descemet’s layer (PDL), generally known as Dua’s layer. He described the three bubble types that are formed when air is injected into a corneo-scleral rim: Type 1, formed between the stroma and PDL; Type 2, between PDL and Descemet’s membrane (DM); and Type 3, a combination of Types 1 and 2.

The demonstration of this layer in paediatric eyes as young as three weeks old confirms the distinctness of this layer, he said. He explained that the consistent path taken by air injected in the cornea, from the initial “cracks in a glass” pattern reminiscent of bacterial colonies travelling within the compact lamellae in infectious crystalline keratopathy, the subsequent circumferential migration along the limbus to the formation of the bubbles, gives information about the anatomy of the cornea. He quoted a paper from Liu et al. that showed that deep fungal filaments follow the coronal plane of this layer and spread along it before penetrating deeper. The PDL merges imperceptibly with the trabecular meshwork at the corneal periphery.

Description of this layer has made deep anterior lamellar keratoplasty (DALK) safer and has led to the innovation of three new surgeries – DALK triple, Pre-Descemet’s endothelial keratoplasty and suture management of acute hydrops (Chérif HY et al.). The 15-20-micron-thick PDL can withstand intraocular pressure up to 700 mmHg.

The Type 1 bubble DALK has a stronger wound than a penetrating keratoplasty and can also withstand the stress of performing a phaco and IOL implantation successfully under this membrane, he said.

Descemet’s detachments can involve both the PDL and the DM, and Descemetoceles have been reported to consist of both the PDL and DM, so these should be looked for. Acute hydrops in keratoconus is most often due to a rupture of the DM and PDL and pre-Descemet’s sutures could be used to resolve acute hydrops.

The role of the PDL in glaucoma, posterior corneal curvature and corneal biomechanics are current hot topics for research, he said. He concluded by informing the delegates that the American Association of Ocular Oncologists and Pathologists had resolved to designate the layer the ‘Dua-Fine layer’ in recognition of his work and the early images presented in the 1979 2nd edition of Ocular Histology: A Text and Atlas, co-authored by Drs Fine and Yanoff.

Harminder Dua:

Dr Dua discussed the discovery of the Dua layer in an Eye Contact interview. See here.